This invention relates to helmet mounted display systems.
More particularly the invention relates to helmet mounted display systems of the kind by which a wearer of the helmet on which the system is mounted is provided with a collimated virtual image of a display produced by a display source superimposed on the helmet wearer's view of a scene through a combiner element of the system.
A known form of such a helmet mounted display system comprises: a helmet having a transparent visor; and an optical system which directs rays of light from a display produced by a display source onto a spherical region of the visor to provide by reflection at the visor, at a helmet wearer's eye position, a collimated virtual image of the display on a line of sight of a wearer of the helmet through the visor. Such a helmet mounted display system is hereinafter referred to as a display system of the kind specified.
It will be appreciated that in a display system of the kind specified the visor serves both as a combiner element and a collimating element to produce the required virtual image. The use of the visor as combiner and collimating elements has the advantage that it avoids the use of a relatively heavy eyepiece combiner and collimating element commonly used in helmet mounted display systems. However, use of the visor as the combiner and collimating elements makes it no longer possible to adapt the system to suit a helmet wearer's eye position by movement of the whole display system.